In a parallel computer in recent years, the necessity for a ring network and a torus network which extended the ring network to multiple dimensions increases. In the parallel computer, a plurality of computing nodes are connected by a network. In the parallel computer, a cost concerning node connection in a network poses a problem as the computing node increases. The ring network is advantageous because the cost concerning connections between many nodes is low.
In the ring network, the cost concerning the node connection is low. Also, the ring network is a symmetrical network. The symmetry of the network is a feature necessary to use the whole network efficiently and equally. Especially, since the parallel calculation program often causes each node to perform regular communication, the symmetry of the network becomes particularly important in the parallel computer. A regular communication pattern is a situation where all network constitution is seen as the same network constitution even if network constitution is seen from any node in the network, and a situation where each node in the network performs data communication by the same algorithm.
On the other hand, the parallel computer is composed of a large number of computing nodes and a small number of input-output node. When the parallel computer calculates, the parallel computer needs to input data from and output data to an external device. An amount of data inputted from and outputted to the external device is generally small, compared with an amount of data transmission between the computing nodes in the parallel computer. For this reason, when input-output devices are attached to only some nodes, a sufficient amount of data can be inputted and outputted. Each of the nodes to which the input-output devices are attached does not generally perform computing, but becomes an input-output node only for input and output of data. When the input-output node which performs input-output processing of data computes, the computing slows, compared with a node which does not perform the input-output processing. In order to perform parallel computing efficiently by the parallel computer, it is important to match the progress of computing and communication of the respective nodes with each other. When the progress of the processing performed by each node has a difference, the efficiency of the parallel computing gets worse.
Conventionally, there has been known a parallel computer with a variable structure distinctive system network in which a plurality of processors are connected by two networks which shared functions (see Japanese Laid-open Patent Publication No. 7-230435). Also, there has been known a parallel computer in which the input-output node is provided on a mesh network (see Japanese Laid-open Patent Publication No. 6-28330).